Your skeletal structure serves two purposes: providing structural support for your muscles and organs, and acting as a repository for essential minerals such as phosphorus, magnesium, and calcium. Your skeleton contains 99% of your body's calcium; the remaining 1% is circulated through your blood and is critical to bodily functions ranging from muscle contraction and nerve functions to blood clotting.
Osteoporosis is the gradual loss of calcium in the structure of your bones, which can be detected as early as age 35. Bones may seem hard and rigid, but your bones are actually alive and changing throughout your whole life. Until the age of 20 or so, bone mass is building and reaches it's peak mass.
Over time though, without proper nutrition and exercise, bone structure thins and becomes much weaker. A person with osteoporosis becomes susceptible to breaking bones and disabling falls. It often goes undetected until a fall or break occurs, when it is too late for medications or other interventions to be of much good. It is one of the leading causes of disability and death in older women, but it also affects men with the same debilitating results.